Development of a statistical lower bound fracture toughness curve

A collection of mechanical property data has been used to develop reference lower bound fracture toughness curves. Many heats of nuclear pressure vessel steel (A533B-1, A508-1, A508-2, A540, A302B, A537-1 and A537-2), heat affected zone material, manual arc and submerged arc weld material were used in the study. Several referencing techniques were used to remove heat to heat variation for a particular material type. The currently employed technique, using RT NDT , was found to inflate variance in some situations instead of reducing it. Alternative and more promising techniques were developed, the best one using the precracked instrumented Charpy impact test. First, mean curves relating the reference test to fracture toughness were developed. Second, the distribution of actual data about the curves was characterised in terms of variance and the form of distribution. Both variance and form of distribution changed with temperature. The results were used to generate a lower bound reference curve (a local tolerance bound), using the function: f = A + B tanh t − T 0 C ( f is normalised fracture toughness and t is normalised temperature).